DE102016110377A1 - A method of making electrical contacts with a silver-tungsten alloy and an electroless / electrolytic electrodeposition of a silver-tungsten alloy - Google Patents

Abstract

The present invention describes a process for the production of electronic components, such as electrical contacts, with a silver-tungsten coating and a basic aqueous-solution electrolyte with silver and tungsten salts for electroless production of a silver-tungsten alloy, the one or more carboxylic acids and / or hydroxycarboxylic acids and / or aromatic carboxylic acids and / or aminocarboxylic acids and / or thiocarboxylic acids and / or sulfonic acid and / or derivatives thereof and / or their sodium or potassium salts, one or more soluble tungsten (VI) salts, one or more soluble silver (I) salts, as well as organic additives (wetting agents and brighteners). The electrolyte and method allow to improve the physico-mechanical properties of silver coating such as hardness, abrasion resistance, while the silver-tungsten alloy maintains a volume resistivity of pure silver coating.

Description

The invention relates to a method for producing an electrical contact element according to the preamble of independent claim 1. The invention also relates to a contact element which is produced by such a method.

Such contact elements are used for the transmission of electrical signals or currents in connectors. Good electrical conductivity and high abrasion resistance are decisive quality features of contact elements.

State of the art

The DE 10 2013 109 400 A1 shows a contact element whose base body is coated in an electrochemical process with a noble metal, for example with a gold or a gold alloy layer.

For some electrode geometries, however, electrodepositions are not always uniform in electrochemical processes. This results in so-called peak or edge effects.

In DE 10 2005 038 208 B4 is a method for the electroless deposition of silver, which uses as complexing agent, amino acids in the amount of 1.0 g / L disclosed. In the DE 10 2005 038 208 B4 the silver coating is deposited in a so-called reduction process.

In the DE10 050 862 A1 describes a process for electroless silver deposition, in which a solution of ethylenediamine, alaninediacetic acid, amino-trimethylphosphonic acid, 1-hydroxyethylene-1,1-diphosphonic acid is used as a complexing agent.

A layer combination of silver and nickel applied in an electroless process (reduction process) is known from US Pat DE 10 2007 053 456 A1 known. The alloy is carried out in a slightly acidic bath at a pH between 4 and 4.65 and contains between 2% and 45% silver.

For the deposition of silver-tungsten alloys on surfaces of workpieces are galvanic baths from the publications US 20 120 118 755 A1 . US 20 120 121 925 A1 and US 20 130 260 176 A1 known.

In electrochemical processes, electricity costs play a not insignificant role in the final price of the coated product.

task

The object of the invention is to propose a method which produces a uniformly good coating on an electrical contact element. The proposed method can also be carried out inexpensively.

The object of the invention is furthermore to propose a contact element which exhibits good electrical properties combined with high abrasion resistance.

The object is solved by the characterizing features of independent claim 1.

Advantageous embodiments of the invention are specified in the subclaims.

To carry out the process according to the invention, a basic electrolyte based on an aqueous solution of silver and tungsten salts is used. The electrolyte is used for electroless / electrolytic production of a silver-tungsten alloy on a body of a contact element.

The electrolyte and the process make it possible to improve the physico-mechanical properties of hitherto known silver coatings, for example hardness, abrasion resistance. The electrical volume resistance of the silver-tungsten alloy according to the invention is comparable to the electrical volume resistance of a pure silver coating.

The inventive electrolyte contains at least one complexing agent, for example a carboxylic acid, an aromatic carboxylic acid, a hydroxycarboxylic acid, an aminocarboxylic acid, a thiocarboxylic acid, a sulfonic acid and / or a mixture of the aforementioned substances in a concentration of 20 to 100 g / liter, but preferably in one Concentration of 40 to 80 g / L. An advantage of the invention is that the abovementioned acids or their salts can also serve as buffers.

Under these conditions, a silver layer thickness of about 0.25 μm was deposited on a base body in two minutes. The tungsten content in the layer was 3.7 mass%. An optical inspection of the surface during a plug-in cycle test showed that the coating did not penetrate until after more than 100 mating cycles.

The coated surface of the contact elements had a roughness (Rz) of 1.9 microns. A comparable pure silver surface has a roughness (Rz) of 5.4 microns.

If the presented purely chemical process is to be operated as an electrochemical process, a current density of 0.8 A / dm ² (+/- 0.2 A / dm ² ) has proven to be advantageous.

The electrolyte described above and used for the electroless process can equally be used for a current-carrying, electrolytic process. It is therefore very advantageous to carry out a two-stage process and first to apply an electroless plating and then to this layer another strombehaftete layer, wherein these two layers are silver-tungsten layers.

An advantage of the method is that no prior activation of the surface or no pre-silvering of the surface must take place before an electrolytic coating, since in the same electrolyte (bath) first a chemical and then an electrolytic silver tungsten deposition can take place.

The method presented here is provided for producing an electrical contact element, wherein the contact element consists of a base body on which at least one coating is applied. The coating is a silver-tungsten alloy deposited by electroless / electrolytic deposition. The main body is preferably made of steel or a copper alloy, for example brass or bronze.

Advantageously, the coating is carried out in an electrolyte whose pH is adjusted between 7.5 and 10, preferably between 8.5 and 9.5. Optimal results were achieved at these pH values.

Advantageously, the electrolyte is supplied with silver ions in the form of their nitrate, acetate, sulfate, lactate or formate salts. In addition, tungsten ions derived from tungsten salts such as sodium tungstate and potassium tungstate are fed to the electrolyte.

Preferably, the silver ions and the tungsten ions, each in a concentration of 5 to 50 grams per liter, but preferably in a concentration of 10 to 40 g / L, are fed to the electrolyte. Optimally, a mass ratio of silver ions to tungsten ions between 2 to 1, to 1 to 2, is set in the electrolyte. These settings provide optimal results.

Preferably, at least one carboxylic acid and / or a hydroxycarboxylic acid and / or an aromatic carboxylic acid and / or an aminocarboxylic acid and / or a thiocarboxylic acid and / or a sulfonic acid and / or a mixture of the abovementioned substances are fed to the electrolyte as complexing agent.

The complexing agent or complexing agents are preferably supplied to the electrolyte in a concentration of 20 to 100 g / L (grams per liter), preferably in a concentration of 40 to 80 g / L.

Preferably, the electrolyte ammonium and / or ammonium salts, preferably ammonium sulfate and / or organic ammonium salts, in a concentration of 10 g / L to 200.0 g / L, preferably in a concentration of 20 to 150 g / L supplied.

In addition, an alkali metal, preferably sodium and / or potassium and / or lithium, in a concentration of 1 g / L to 60 g / L, preferably in a concentration of 1 g / L to 30 g / L, are added to the electrolyte.

Furthermore, it is advantageous if the electrolyte molybdenum ions in a concentration of 0.5 g / L to 20 g / L, preferably in a concentration of 1 to 10 g / L, are supplied.

In a preferred embodiment of the invention, at least one wetting agent in a concentration of 0.01 to 5 g / L, preferably in a concentration of 0.05 to 1 g / L, is supplied to the electrolyte.

In a particularly preferred embodiment of the invention, the electrolyte is operated at a temperature of 20 to 60 ° C, but preferably at a temperature of 30 to 45 ° C. These temperature ranges can be easily set and monitored.

Advantageously, the residence time of the contact element in the electrolyte is from 15 seconds to 5 minutes, but preferably from 30 seconds to 3 minutes for the electroless process and to 5 minutes for the electrolytic process. The specified upper or lower time limit is contained in the respective time interval.

With the method presented above, electrical contact elements are produced or the surface of a main body of a contact element or of an already precoated contact element is coated.

The electrical contact element according to the invention consists of a base body, which with at least one coating is provided, wherein at least one coating consists of a silver-tungsten alloy.

Advantageously, the body of the contact element is provided with at least two coatings, a lower and an upper coating, and the lower coating is a nickel layer or a nickel alloy layer or a copper layer or a copper alloy layer and the upper layer is the silver-tungsten alloy deposited thereon.

However, the silver-tungsten alloy is the electrically conductive and abrasion-resistant top coating of the contact element in all variations.

It is advantageous if the tungsten content of the silver-tungsten alloy is at most 10 percent by weight, but preferably from 1 to 6 percent by weight, but more preferably from 1 to 4 percent by weight.

In the electroless method, the silver-tungsten layer thickness is preferably 0.05 to 0.5 micrometers, but preferably 0.05 to 0.3 micrometers. The start and end values of the specified layer thickness intervals are explicitly included. In the electrolytic method, the thickness of the deposited silver-tungsten alloy is 0.05 to 5 micrometers, more preferably 0.05 to 3 micrometers.

Virtually no disadvantages could be observed in the silver-tungsten electrolyte according to the invention. The deposited silver-tungsten alloy has a volume resistivity comparable to a corresponding pure silver layer. In addition, the deposited silver-tungsten alloy has at least 60% higher microhardness than the corresponding pure silver layer. Dependent on the tungsten content, the microhardness of the silver-tungsten alloy ranges from 240 to 260 HV. A comparable silver layer has a microhardness of 120 to 160 HV.

In addition, the layers made from baths according to the invention showed advantageous mechanical properties. Thus, a throughdrift of the about 0.25 micron thick silver tungsten layer with about 3.5 wt.% Tungsten was only after 125 mating cycles. By comparison, the pure silver layer was rubbed through after 50 mating cycles, even though the layer thickness was three micrometers. In the electrolytic process and a silver-tungsten layer thickness of about 2.0 microns with about 3.0 wt.% Tungsten, the penetration was only between 1000 to 2500 mating cycles. The abrasion resistance of the electrodeposited silver-tungsten alloy is at least 10 times higher than the abrasion resistance of the corresponding pure silver layer.

example

The silver-tungsten electrolyte consists essentially of:
30 g / L silver as silver nitrate
30 g / L sodium tungstate
80 g / L Na salt aminocarboxylic acid
15 g / L citric acid

The working parameters are essentially:
pH value: 8.5
Current density: 0.8 A / dm ²

At a working temperature of 40 ° C, a silver layer thickness of about 0.25 μm was deposited on the workpiece for two minutes. The tungsten content in the layer was 3.7% by mass.

In the subsequent plug-in cycle tests (resistance to abrasion), the coating did not penetrate until after more than 100 mating cycles. The silver-tungsten coating on the workpieces, which were in the form of turned contact elements, had a roughness (Rz) of 1.9 μm. By contrast, a comparable pure silver surface has a roughness (Rz) of 5.4 μm.

An electrical contact element made by the above method comprises a silver-tungsten alloy having a volume resistivity comparable to a corresponding pure silver layer.

The microhardness of the silver-tungsten alloy is from 240 to 260 HV, the microhardness of a comparable pure silver layer being from 120 to 160 HV. Here, a known Vickers hardness test was used. The specified boundary values are included in the hardness interval.

The layer thickness of the deposited silver-tungsten alloy is from 0.05 to 0.5 micrometers, preferably from 0.05 to 0.3 micrometers, with the deposited in the electroless method silver-tungsten alloy at a layer thickness of 0.25 μm has a comparable through resistance as a comparable pure silver layer with a layer thickness of 3.0 micrometers.

The abrasion resistance of the deposited silver-tungsten alloy is at least two times higher than the abrasion resistance of a corresponding pure silver layer.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102013109400 A1 [0003]
• DE 102005038208 B4 [0005, 0005]
• DE 10050862 A1 [0006]
• DE 102007053456 A1 [0007]
• US 20120118755 A1 [0008]
• US 20120121925 A1 [0008]
• US 20130260176 A1 [0008]

Claims (26)

Method for producing an electrical contact element, wherein the contact element consists of a base body on which at least one coating is applied, characterized in that the at least one coating is a silver-tungsten alloy. Method for producing an electrical contact element according to Claim 1, characterized in that at least one further layer is applied to the base body and the further layer is a nickel layer, a nickel alloy layer, a copper layer, a copper alloy layer. A method for producing an electrical contact element according to claim 1, characterized in that the silver-tungsten alloy by an electroless deposition (charge exchange method) is applied. Process for producing an electrical contact element according to one of Claims 1 to 3, characterized in that the coating bath in the basic range is in a pH range of 7.5 to 10, but preferably in a pH range of 8.5 to 9, 5, is set. Process for producing an electrical contact element according to one of the preceding claims, characterized in that - silver ions in the form of their nitrate, acetate, sulfate, lactate or formate salts are fed to the coating bath, and tungsten ions of sodium tungstate and / or potassium tungstate are added to the coating bath, be supplied. Process for producing an electrical contact element according to one of the preceding claims, characterized in that the coating bath according to the invention tungsten ions derived from tungsten salts, for example, sodium tungstate and potassium tungstate, in a concentration between 5 to 50 grams per liter, but preferably in a concentration of 10 up to 40 grams per liter. Method for producing an electrical contact element according to one of the preceding claims, characterized in that in the coating bath, a mass ratio of silver ions to tungsten ions between 2 to 1 to 1 to 2, is set. A process for producing an electrical contact element according to any one of the preceding claims, characterized in that the coating bath as a complexing agent at least one carboxylic acid and / or a hydroxycarboxylic acid and / or an aromatic carboxylic acid and / or an aminocarboxylic acid and / or a thiocarboxylic acid and / or a sulfonic acid and / or a mixture of the aforementioned complexing agents are supplied. A process for producing an electrical contact element according to the preceding claim, characterized in that the complexing agent or the complexing agent to the coating bath in a concentration of 20 to 100 g / L, preferably in a concentration of 40 to 80 g / L, are supplied. A process for producing an electrical contact element according to any one of the preceding claims, characterized in that the coating bath, a sodium or potassium salt of the carboxylic acid, a hydroxycarboxylic acid, an aromatic carboxylic acid, an aminocarboxylic acid, a thiocarboxylic acid, a sulfonic acid or a mixture of the aforementioned substances in a concentration from 20 to 100 grams per liter, but preferably at a concentration of 40 to 80 grams per liter. Process for producing an electrical contact element according to one of the preceding claims, characterized in that the coating bath ammonium and / or ammonium salts, such as ammonium sulfate or / and organic amine salts, in a concentration of 10 to 200 grams per liter, but preferably in a concentration of 20 to 150 grams per liter, is supplied. A process for producing an electrical contact element according to any one of the preceding claims, characterized in that the coating bath, an alkali metal, preferably sodium and / or potassium and / or lithium, in a concentration of 1 g / L to 60 g / L, preferably in a concentration from 1 g / L to 30 g / L. Process for producing an electrical contact element according to one of the preceding claims, characterized in that molybdenum ions in a concentration of 0.5 g / L to 20 g / L, preferably in a concentration of 1 to 10 g / L, are supplied to the coating bath. Method for producing an electrical contact element according to one of the preceding claims, characterized in that the coating bath has at least one wetting agent in one Concentration of 0.01 to 5 g / L, preferably in a concentration of 0.05 to 1 g / L, is supplied. A method for producing an electrical contact element according to any one of the preceding claims, characterized in that in the coating bath, the tungsten content of the silver-tungsten alloy at a maximum of 10 weight percent, but preferably from 1 to 6 weight percent, more preferably from 1 to 4 weight percent is set , Method for producing an electrical contact element according to one of the preceding claims, characterized in that the coating bath is operated at a temperature of 20 to 60 ° C, but preferably at a temperature of 30 to 45 ° C. Method for producing an electrical contact element according to one of the preceding claims, characterized in that the deposition of the silver-tungsten alloy is operated in an electrolytic process by means of direct current or pulse current. Method for producing an electrical contact element according to the preceding claims 3 and 17, characterized in that the silver-tungsten alloy is first deposited without current and then further deposited in an electrolytic process by means of direct current or pulse current. Process for producing an electrical contact element according to the preceding claim, characterized in that in the electrolytic process, the current density of 0.1 to 2.0 A / dm2, but preferably from 0.5 to 1.5 A / dm2, is set. A method for producing an electrical contact element according to any one of claims 18-19, characterized in that the electroless plating of 15 seconds to 5 minutes, but preferably of 30 seconds to 3 minutes and then the electrolytic coating of 15 seconds to 10 minutes, but preferably from 1 minute to 6 minutes. Method for producing an electrical contact element according to one of the preceding claims, characterized in that the silver-tungsten alloy in the electroless plating in a thickness of 0.05 to 0.5 micrometers, in particular in a thickness of 0.05 to 0, 3 microns, is applied. A method for producing an electrical contact element according to any one of claims 18-21, characterized in that the silver-tungsten alloy in the electrolytic coating in a thickness of 0.05 to 0.5 microns, in particular in a thickness of 0.05 to 0.3 microns, is applied. An electrical contact element produced by a method according to any one of the preceding claims, characterized in that the deposited silver-tungsten alloy has a volume resistivity comparable to a corresponding pure silver layer. Electrical contact element according to the preceding claim, characterized in that the microhardness of the silver-tungsten alloy is from 240 to 260 HV, the microhardness of a comparable pure silver layer being from 120 to 160 HV. Electrical contact element according to one of the two preceding claims, characterized in that the layer thickness of the deposited silver-tungsten alloy from 0.05 to 0.5 micrometers, preferably from 0.05 to 0.3 micrometers, which in the electroless method deposited silver-tungsten alloy at a layer thickness of 0.25 microns has a comparable through resistance as a comparable pure silver layer at a layer thickness of 3.0 microns. A method for producing electrical contacts with a silver-tungsten alloy according to any one of claims 1 to 18, characterized in that the abrasion resistance of the deposited silver-tungsten alloy is at least two times higher than the abrasion resistance of a corresponding pure silver layer.